The invention relates to wireless communication systems and, more particularly, to the assignment of burst transmissions in such systems.
Wireless communication systems have been developed to allow transmission of information signals between an originating location and a destination location. Both analog (first generation) and digital (second generation) systems have been used to transmit such information signals over communication channels linking the source and destination locations. Digital methods tend to afford several advantages relative to analog techniques, including, e.g., improved immunity to channel noise and interference, increased capacity, and improved security of communication through the use of encryption.
While first generation systems were primarily directed to voice communication, second generation systems support both voice and data applications. Numerous techniques are known in second-generation systems for handling data transmissions which have different transmission requirements. Several modulation/coding arrangements have been developed for wireless systems based on multiple access techniques, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA). In FDMA techniques, each user is allocated one or more specific sub-bands of frequency. In TDMA techniques, periodically recurring time slots are identified, and for each segment of time each user is allocated one or more time slots. CDMA systems provide reduced multiple path distortion and co-channel interference and reduce the burden of frequency/channel planning that is common with FDMA and TDMA systems.
In a CDMA system, a unique binary spreading sequence (a code) is assigned for each call to each user. Multiplied by the assigned code, the user""s signal is spread unto a channel bandwidth much wider than the user signal bandwidth. The ratio of the system channel bandwidth to the user""s bandwidth is commonly called the spreading gain. All active users share the same system channel bandwidth frequency spectrum at the same time. Calculating the signal-to-interference ratio (SIR) determines the connection quality of the transmission link. Given a required SIR, the system capacity is proportional to the spreading gain. The signal of each user is separated from the others at the receiver by using a correlator keyed with the associated code sequence to de-spread the desired signal.
First-generation analog and second-generation digital systems were designed to support voice communication with limited data communication capabilities. Third-generation wireless systems, using wide-band multiple access technologies such as CDMA, are expected to effectively handle a large variety of services, such as voice, video, data and imaging. Among the features which will be supported by third-generation systems is the transmission of high-speed data between a mobile terminal and a land-line network. As is known, high-speed data communications is often characterized by a short transmission xe2x80x9cburstxe2x80x9d at a high data transmission rate, followed by some longer period of little or no transmission activity from the data source. To accommodate the bursty nature of such high-speed data services in third-generation systems, it is necessary for the communications system to assign a large bandwidth segment (corresponding to the high data rate) from time to time for the duration of the data burst. With the ability of the third generation systems to handle such bursty high-speed data transmission, throughput and delay for users can be advantageously improved. However, because of the large amount of instantaneous bandwidth required for transmission of a burst of high-speed data, the management of such bursts, and particularly the allocation of power and system resources thereto, must be handled with care to avoid unwarranted interference with other services using the same frequency allocation. Consequently, system designers need to deal with many issues in setting efficient data rates for different types of communications via a wireless link, including appropriate allocation of system resources for the bursts of data experienced with high-speed data service.
There is a continuing need to increase the performance and improve the throughput of wireless communication systems. In particular, there is a need for an improved burst duration assignment methodology such that resources are efficiently utilized in a communication system such as CDMA.
There is also a need to avoid overhead and power-overload problems in burst duration assignment for communication systems.
The invention provides a novel burst duration management process that increases the performance and the throughput of wireless communication systems. In particular, the invention provides an improved burst duration assignment methodology that results in an efficient utilization of resources in a communication system such as one based on CDMA. According to the invention, burst duration is assigned in relation to channel fading fluctuation and user mobility in the communication system. In general, a short burst duration is assigned to users with high fading fluctuation and/or high mobility. A long burst duration is assigned to users with low fading fluctuation and/or low mobility. In a particular embodiment of the invention, the burst assignment is based on a function of duration versus fluctuation. The invention advantageously avoids overhead and power-overload problems in burst duration assignment for both the forward link and the reverse link in wireless communication systems. The invention also avoids problems due to changing conditions such as user mobility and fading during a burst duration assignment.